Critical Care Trauma Centre

COLD CARDIAC OUTPUTS: USING CO-SET

Cardiac Output measurements
are done in CCTC using the closed system CO-Set. Cold injectate (6-120
C is the standard method); room temperature D5W 18-250 C can
be used with the same circuit if myocardial irritation is detected (ectope,
chest pain during injections).

Measurement of
C.O. with a right heart catheter is done using the thermodilution technique:

A known
volume of D5W that is colder than blood temperature is injected into the
right atrial port of the catheter.

The
injectate solution temperature is measured prior to injection.

The
blood temperature is measured in the pulmonary artery.

The
D5W injection enters the right atrium and lowers the right atrial blood
temperature.

The
cooler right atrial blood is ejected to the pulmonary artery, where the
temperature change is detected by the thermistor in the pulmonary artery.

A temperature
curve over time is created as the pulmonary artery temperature initially
falls, then rises back to normal as warmer blood replaces the cooled injectate
solution (the "Y" axis plots temperature in decreasing increments).

The
computer "knows" the volume, temperature and catheter lumen size by the
computation constant that is entered. Based on this information,
the cardiac output program can calculate the amount of blood pumped per
minute for a given temperature change over time.

The
computation constant varies according to the catheter style, volume of
injectate to be used, and temperature of injectate solution. Use
of the correct computation constant is essential to ensuring accurate results.
Cardiac output is determined by calculating the change in temperature over
the change in time. A change in the model, or injectate volume
or temperature will alter the expected temperature change at various cardiac
outputs; the correct algorhythm is "selected" by the computer program by
entering the computation constant.

Model of Right Heart Catheter (Baxter)

Temperature of
Injectate

Volume of Injectate

Computation Constant

VIP

18
- 25oC

10
mL

0.592

VIP

6
- 12oC

10
mL

0.578

Paceport

18
- 25oC

10
mL

0.592

Paceport

6
- 12oC

10
mL

0.578

Regular (4 lumen)

18
- 25oC

10
mL

0.608

Regular (4 lumen)

6
- 12oC

10
mL

0.561

SVO2

18
- 25oC

10
mL

0.607

SVO2

6
- 12oC

10
mL

0.553

AV Paceport

18
- 25oC

10
mL

0.608

AV Paceport

6
- 12oC

10
mL

0.561

RHEF (blue port)

6
- 12oC

10
mL

0.561

Model of Right Heart Catheter
injectate

Temperature of
Injectate

Volume of Injectate

Computation Constant

VIP

8
- 16oC

5
mL

0.272

Paceport

8
- 16oC

5
mL

0.272

Regular (4 lumen)

8
- 16oC

5
mL

0.259

SVO2

8
- 16oC

5
mL

AV Paceport

8
- 16oC

5
mL

RHEF (blue port)

8
- 16oC

5
mL

*N.B. ALWAYS REGARD
THE BLUE PORT AS THE INJECTION LUMEN OF THE VIP MODEL. HOWEVER, SHOULD
THE BLUE LUMEN BECOME PLUGGED YOU MAY USE THE WHITE PORT TO INJECT THROUGH,
USING THE SAME COMPUTATION CONSTANT.

Procedure

Rationale

1.Measurement
of C.O. with a right heart catheter is done using thermodilution technique,
where temperature is the detected change.

1.Injection of
a predetermined amount of fluid, at a known T., into C.V.P. port provides
the temperature change/change in time signal that the computer analyzes
to calculate CO.

2.Cold cardiac
outputs are measured using 10 mL of 6-12oC D5W. Variations in volume, catheter,
or temperature may require a change to the constant used (see chart for
cardiac output constants).

19.The infusion
sits between the injectate and patient. Any variation between the temperatures
of the CVP infusion and the cardiac output injectate would alter temperature
after injectate temperature is measured.

20.Unclamp the
D5W line of the Closed Injectate Delivery System.

20.Filling will
begin automatically upon release of clamp.

21.Withdraw 10
mL of D5W into the syringe. Close the clamp as soon as filling is complete.

Note: if you pull
back on the syringe plunger too hard the plunger can actually be pulled
out of the syringe. Be careful not to over fill.

21.When the clamp
is opened, the syringe will continue to fill.

D5W is the required
solution because calculation of cardiac output is based on the specific
gravity and temperature of blood, and specific gravity and temperature
of D5W (NaCl has a different specific gravity).

A one way valve
prevents aspiration of blood or backward flow during syringe filling.

22.Press start CO.Inject when monitor displays "Inject Now".

22.To activate
program.

23.Perform injection
as exhalation begins. If the patient is receiving any mechanical ventilation,
perform the injection with a mechanical breath.

23.Allows for
minimal variation related to different phases of the respiratory cycle.
Venous return and filling pressures change at various points of the respiratory
cycle. Mechanical breaths will have the greatest influence.

25.Calculation
of cardiac output depends on the difference between patient's blood temperature
and injectate temperature.

Injection must
take place in order to detect temperature accurately.

26.Ensure that
the temperature of the injectate is between 6-12oC.

26.To ensure
temperature is within range.

27.Perform a
minimum of 3 measurements and obtain the average.

Space injections
approximately 1 minute apart.

Discard all samples
with a variance of more than 10% from other measurements.

Discard samples
with a poor quality curve by editing, then averaging results. Remove inaccurate CO by scrolling to "Edit results", once this is complete press "average all", then it will ask you to press "confirm".

27.Waiting a
minute between injections permits blood temperature to return to normal
between measurments.

To prevent averaging in inaccurate results.

28.Remove the
Flow-Through temperature probe from the housing.

28.To prevent
damage to cable during patient turning etc.

29.Open IV stopcock
and restore infusion rate.

29.To ensure
IV therapy resumes and line patency is maintained.

30.Ensures PAP
tracing is present on monitor when completed.

30.To establish
catheter placement has not been altered.

31. Remove non-sterile gloves and perform hand hygiene.

31. In accordance with the MoHLTC 4 moments of hand hygiene and LHSC infection control policies.

32.Simultaneous
measurements are important when calculations for oxygen extraction, O2
delivery, and O2 consumptions are done. Oxygen delivery for example is
calculated as C.O. x Arterial Oxygen Content, the assumption is that all
factors in the equation reflect the same time and condition.

Unless bleeding,
Hb does not change very quickly. Hb is needed to calculate oxygen content
and therefore any values using oxygen content.

Lactates are invalid
if a tourniquet is applied as the distal limb would produce increased lactic
acid.

32.Obtain venous
and arterial gases, lactate and Hb. Both gases must be drawn within 5 minutes
of cardiac output measurement. The same conditions must exist during cardiac
output and blood gas measurements (ie. head of bed at same level, same
oxygen concentration and same amount of ventilation).

Unless actively
bleeding, the Hb should be drawn within 4 hours of the Cardiac output measurement.

The lactate should
be drawn within 4 hours of the cardiac output measurement. Either an arterial
or venous lactate may be sent. Venous lactates must be drawn from an indwelling
catheter (no tournequet).

33.Identify B.S.A.
using B.S.A. guide.

33.Cardiac index
standardizes the body surface area so that the normal range for CI is the
same for all patients.

34.Identify the
patient's FI02.

34.FI02 is needed
for the computer to calculate shunt (QS/QT).

35.Enter the
collected data into the CCTC computer program

"Critbase".

35.Critbase
will calculate the pre-programmed equations for the desired hemodynamic
variables and oxygen transport indices.

36.Double check
the data you have entered on the hemodynamic profile for typographical
errors.

36.Since most
of the values are calculated by the entered information, incorrect data
will result in multiplied errors for the calculated values.

37.Have the results
reviewed by the physician.

37.To determine
therapy and communicate results.

38.Place profile
on the back of the physician's clinical notes and record appropriate hemodynamic
data onto flowsheet.